diff --git a/core/lib/Drupal/Core/Http/HandlerStackConfigurator.php b/core/lib/Drupal/Core/Http/HandlerStackConfigurator.php
index d5aa3c5..b08717f 100644
--- a/core/lib/Drupal/Core/Http/HandlerStackConfigurator.php
+++ b/core/lib/Drupal/Core/Http/HandlerStackConfigurator.php
@@ -29,20 +29,47 @@ class HandlerStackConfigurator {
    *
    * @var callable[]
    */
-  protected $middlewares = [];
+  protected $middlewares = NULL;
+
+  /**
+   * A list of used middleware service IDs.
+   *
+   * @var string[]
+   */
+  protected $middlewareIds;
+
+  /**
+   * The service container.
+   *
+   * @var \Symfony\Component\DependencyInjection\ContainerInterface
+   */
+  protected $container;
 
   /**
    * Contructs a new HandlerStackConfigurator object.
    *
    * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
    *   The service container.
+   * @param string[] $middleware_ids
+   *   The middleware IDs.
    */
   public function __construct(ContainerInterface $container, array $middleware_ids) {
-    foreach ($middleware_ids as $middleware_id) {
-      $middleware = $container->get($middleware_id);
-      if (method_exists($middleware, '__invoke')) {
-        $class = get_class($middleware);
-        $this->middlewares[$middleware_id] = $class();
+    $this->middlewareIds = $middleware_ids;
+    $this->container = $container;
+  }
+
+  /**
+   * Ensures that the middlewares are initialized.
+   */
+  protected function initializeMiddlewares() {
+    if (!isset($this->middlewares)) {
+      $this->middlewares = [];
+      foreach ($this->middlewareIds as $middleware_id) {
+        $middleware = $this->container->get($middleware_id);
+        if (method_exists($middleware, '__invoke')) {
+          $class = get_class($middleware);
+          $this->middlewares[$middleware_id] = $class();
+        }
       }
     }
   }
@@ -54,6 +81,7 @@ public function __construct(ContainerInterface $container, array $middleware_ids
    *   The handler stack
    */
   public function configure(HandlerStack $handler_stack) {
+    $this->initializeMiddlewares();
     foreach ($this->middlewares as $middleware_id => $middleware) {
       $handler_stack->push($middleware, $middleware_id);
     }
diff --git a/core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php b/core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php
index b7a0421..1a7870c 100644
--- a/core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php
+++ b/core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php
@@ -102,10 +102,10 @@ public function fetch(FeedInterface $feed) {
 
       $feed->source_string = (string) $response->getBody();
       if ($response->hasHeader('ETag')) {
-        $feed->setEtag($response->getHeader('ETag')[0]);
+        $feed->setEtag($response->getHeaderLine('ETag'));
       }
       if ($response->hasHeader('Last-Modified')) {
-        $feed->setLastModified(strtotime($response->getHeader('Last-Modified')[0]));
+        $feed->setLastModified(strtotime($response->getHeaderLine('Last-Modified')));
       }
       $feed->http_headers = $response->getHeaders();
 
diff --git a/core/modules/locale/locale.batch.inc b/core/modules/locale/locale.batch.inc
index f549e51..42d0e8d 100644
--- a/core/modules/locale/locale.batch.inc
+++ b/core/modules/locale/locale.batch.inc
@@ -249,7 +249,7 @@ function locale_translation_http_check($uri) {
       $result['location'] = $actual_uri;
     }
 
-    $result['last_modified'] = $response->hasHeader('Last-Modified') ? strtotime($response->getHeader('Last-Modified')[0]) : 0;
+    $result['last_modified'] = $response->hasHeader('Last-Modified') ? strtotime($response->getHeaderLine('Last-Modified')) : 0;
     return $result;
   }
   catch (RequestException $e) {